This invention relates to a method and apparatus for determining the characteristics of seeds prior to germination.
At present, a common method of determining seed germination (defined as growth of the embryo) consists of planting a predetermined number of seeds in light soil or wet toweling and determining the percent with radicle emergence after a fixed interval of time, usually seven days or more. This laboratory germination test is intended to indicate the field planting value of a seed sample (International Rules for Seed Testing, 1966). Some samples of seeds, however, show a marked discrepancy between laboratory germination and field emergency. Several attempts have been made in the past to develop tests that would better indicate the field emergency of seed samples such as germination tests in unsterilized soil and in compost. However, these tests are difficult to standardize and take several days to complete. See the articles by S. Matthews and W. T. Bradnock, Proc. Int. Seed Test. Ass. Vol. 32 (1967) No. 3, po. 553,563, and Hort. Res., 1968, Vol. 8 pp. 89-93. In search for a better and shorter test, these authors describe a 24 hour exudation test as a basis for predicting field performance. They report the discovery of a significant negative correlation between the field emergency of seed samples of peas and French beans and the readiness with which seeds from the samples yielded electrolytes to seed-steep water. They found that the samples that exuded electrolytes readily, as measured by the electrical conductivity of seed-steep water after 24 hours, gave low emergency counts in the field. They also found that in the case of peas a similar relation existed between emergence and the exudation of soluble carbohydrates. More recent work of this nature is reported by D. A. Perry and J. C. Harrison in Journal of Experimental Botany, Vol. 21, No. 67, pp. 504-12, May, 1970.
Various methods have been proposed heretofore for determining the germinating value of seeds, most of which destroy the test seeds. For example in U.S. Pat. No. 1,330,112-Gallardo there was proposed a method of determining the germinating value of seed by subjecting selected seeds to the action of a reagent which causes a contrasting difference in color between the fit or sound portions and the unfit or unsound portions of the seed. U.S. Pat. No. 2,921,598 to Aegidius there is disclosed an apparatus for determining the germination capacity of seed utilizing a reaction vessel in which selected grains after having been split longitudinally through the embryo are exposed to a reaction with an aqueous solution of a compound which causes a dyeing of the embryo if capable of germinating. In U.S. Pat. No. 3,530,372 - Laukien there is disclosed a method for automatically non-destructively testing plant seeds and sorting the seeds on the basis of the content of a specific substance, such as, e.g., water, oil, etc. The weight of a particular seed and the amount of the given substance contained in it are determined automatically, from which the specific content of the substance of the seed is calculated automatically, whereupon suitable seeds are selected using as the criterion whether the specific content is greater than a predescribed desired value.
Another test that has been applied to seeds over the years is the test for moisture content in storage; however, this is not a test for germination or field emergence. Electric moisture meters for indicating moisture in stored grains have been known for a number of years. One of the early electric moisture meters is disclosed in U.S. Pat. No. 1,059,099 - A. Zeleny (1913). Another apparatus of the electrical type for determining moisture in stored seeds and grains is disclosed in U.S. Pat. No. 2,825,870 - Hart. In the Yearbook of Agriculture "Seeds" (1961), Ways to Test Seeds for Moisture, Lawrence Zeleny points out at page 447 that factors other than moisture content affect the electrical properties of seed, and a more thorough understanding of these factors will be required before any appreciable increase in accuracy of electric moisture-testing methods can be expected.
The need for determining the potential viability of seeds is more clearly understood when it is realized that a seed grower may have a stock pile of several tons of seeds to be placed on the commercial market. If he finds, however, that the level of viability in this particular batch of seeds is lower than a prescribed standard germination level, set down by Government spedifications, then the entire batch of seeds has to be discarded. If however, a method is available for non-destructively separating out the non-viable seeds, then obviously a high percentage of the stock pile of seed could be saved for distribution.
U.S. Pat. No. 3,852,914 to Levengood discloses a recent development in which the viability of the seeds were predicted by contacting each individual seed with an electrode pair and measuring the electrical current passing through the seed. In such a manner, the seeds can be separated into groups according to their measured values of electrical current which correlates to their potential viability and vigor. While this method has proved to be extremely satisfactory, it, unfortunately, is extremely time consuming since each seed must be individually contacted by the electrodes.